All About Series | September 6, 2023
All About Electric School Bus Battery Safety

The innovative batteries that power electric school buses meet rigorous safety standards, are extensively tested and are ready to power the ESB transition.

A person works on the type of battery often used in electric school buses.

There’s nothing more important than keeping children safe and healthy on their ride to and from school. At its core, that’s what the electric school bus transition is all about.

Remarkable advances made in battery technology in recent years are powering this transition, allowing zero-tailpipe-emissions electric school buses to safely transport students over a variety of routes in a range of conditions. 

As with any new technology, it’s good to dig into the evidence to learn how it works. When it comes to the batteries inside electric school buses, there are a few key things to know:

  • Electric school bus batteries are designed and built to be safe
  • Electric school bus batteries are extensively tested
  • Electric school bus batteries have rigorous safety mechanisms built in
  • Electric school bus safety training for technicians and first responders is always a good idea

Electric school buses are as safe or safer than fossil fuel-burning buses

All school buses are designed to be safer than any other passenger vehicle type and are the most regulated vehicles on the road, required to meet more Federal Motor Vehicle Safety Standards than any other vehicle. They also have added protection from other motorists through a series of stopping laws and safety features such as flashing lights, cross-view mirrors, and highly visible coloring.

One particular area of focus is the prevention of school bus fires – also called “thermal events” – especially related to the internal combustion engines in fossil fuel-burning school buses and the batteries in electric school buses. Due to extensive safety standards, school bus fires are very rare. Bus fires, including for school buses, accounted for only 1% of all vehicle fires in 2021, none of which involved electric school buses. And there were zero bus-fire-related deaths reported to the National Fire Incident Reporting System, according to the most recent tracking. 

While extremely rare, school bus fires are possible with any type of school bus. But the batteries in electric school buses are less likely to catch fire than the internal combustion engines used in diesel-burning and propane-burning school buses. In other words: according to the statistics, gasoline or diesel vehicles are more likely to catch fire than electric vehicles. 

In a report detailing hundreds of thousands of vehicles over years on the road, the Swedish government’s Authority for Social Protection and Preparedness found that gas- and diesel-burning passenger vehicles have a 1 in 1,300 chance of catching fire, compared to a 1 in 38,000 chance of fire for electric vehicles and hybrids indicating that fossil fuel-burning passenger vehicles are 29 times more likely to catch fire. And a study from RWTH Aachen University in Germany found the failure rate of electric vehicles to be around 0.9 to 1.2 per 10,000 vehicles, compared to 7.3 per 10,000 fire accidents with fossil fuel-burning passenger vehicles in the U.S. 

Further, the National Fire Protection Association reports that two thirds of all vehicle fire deaths result from fires that begin with flammable or combustible liquid or gas, and gasoline or diesel fuel is first ignited in more than half of all highway vehicle deaths. Electric school buses don’t have internal combustion engines or diesel or gasoline fuel, mitigating this risk entirely.

The batteries in electric school buses are less likely to catch fire than the internal combustion engines used in diesel-burning and propane-burning school buses

Electric school bus batteries are extensively tested and have rigorous safety mechanisms

While the batteries in electric vehicles are inherently less likely to cause fires than internal combustion engines, there are also a number of additional aspects that make electric school bus batteries safe for use – including the use of globally-recognized testing standards and advanced safety features.

  1. Extensive battery testing: Battery testing is essential in identifying and developing solutions for problems before they occur. ESB batteries follow globally-recognized automotive safety standards, so batteries are subject to very high safety standards. These include safety-specific standards for the batteries (SAE J2929) and the systems in the vehicle that monitor and control the batteries (ISO 26262). Additionally, there are UL and UN safety certifications for lithium-ion batteries that need to be completed by the cell manufacturer before it is sold. These tests are industry standards and must be passed for the vehicle to be certified for sale.  
  2. Typical ESB battery chemistry offers additional stability: Battery safety starts with battery chemistry. LFP (Lithium-iron-phosphate) batteries used in almost all electric school buses have better thermal stability compared to NMC (nickel-manganese-cobalt) batteries commonly used in electric cars. This thermal stability ensures that the battery structure remains intact for longer than for electric cars even during high temperatures and decreases the chances that fires spread.
  3. Solid battery protection: The structural placement of the electric school bus battery is designed with safety in mind. Battery packs are typically enclosed in a weather-durable metal casing and laid in between the guard rails of the bus chassis for maximum protection. This area is often referred to as the vehicle’s safe zone as it is separated from passengers by a structural barrier and away from the front of the bus where collisions are more common. This is intended to protect against adverse physical impacts to the battery – including dislocation and disfiguration, impacts from weatherization, and theft.
  4. Automatic Electrical Disconnects: ESBs are designed with automatic electrical disconnects that activate in a moderate or severe crash event or if the electrical system short circuits. This mechanism breaks the conductive connection between the battery and electric motor to prevent fires. Further, if the automatic disconnect fails, ESBs have manual cutoff switches to isolate the battery and disable the electrical system.
  5. Battery management system and Passive Propagation Resistance: The battery management system provides an added layer of safety by controlling the temperature of the battery pack to remain in its most optimal state of performance. ESBs have specific protection to maintain the battery temperature – an active cooling system in electric school buses helps maintain an optimal temperature around the battery, and a secondary safety system automatically shuts off the battery before major issues can arise. ESB batteries are equipped with Passive Propagation Resistance (PPR). This safety system is designed to detect and isolate single battery cells experiencing a rare thermal incident. PPR prevents the issue from spreading to neighboring battery cells and triggers a slower release of energy to allow for more efficient heat venting. 
  6. Roll Over Resistance: The stability of an electric school bus provides roll over mitigation. Most vehicle fire deaths result from fires caused by collisions or roll overs. According to the National Fire Protection Association, roll overs occur in only 1-3% of all motor vehicle crashes but account for nearly one third of all passenger fatalities. Electric school buses are less likely to roll over because the location of the battery in the base of an electric school bus lowers the vehicle’s center of gravity and reduces its roll over risk during a crash.

Electric school buses are designed with automatic electrical disconnects that activate in a moderate or severe crash event or if the electrical system short circuits

Training can make electric school buses even safer

Despite these safety measures, there remains a small risk of fires while working with high-voltage components. Because electric vehicles are newer technology and the rare fires associated with EV batteries can have a number of effects – including arcing, ejected metal and conductive soot – it's important that technicians and first responders be prepared. There are several ways to mitigate the harm that may come from these potential events: 

  1. Training for bus operators and maintenance staff: Fire and safety training for operators and maintenance personnel should be provided by the bus manufacturer, dealer, and/or the state pupil transportation association. Maintenance technicians need to be provided with suitable training, personal protective equipment and tools for handling high voltage batteries. School districts may should also consider installing fire detection systems to reduce risk.  
  2. Early engagement with first responders: It is beneficial to notify local first responders early in the ESB planning process. This would give them time to train staff, get the necessary emergency response guides from the vehicle manufacturers and offer recommendations on site safety. The National Fire Protection Association (NFPA) has useful resources to help local first responders best prepare for any battery incidents:
    1. Training course for Emergency Responders which meet recommendations from the National Transport Safety Board (NTSB). The training is open to anyone who may respond to incidents involving alternative fuel vehicles (electric, propane, CNG), including fire service, emergency medical service technicians, crash reconstruction, and tow and salvage personnel.
    2. International Association of Fire Chiefs bulletin on responding to EV fires. 
    3. Quick reference flyer on EV fires from NFPA.
    4. American Public Transportation Association recommendations for fire/thermal incident investigation
    5. SAE International Hybrid and EV First and Second Responder Recommended Practices.

To learn more about how to make electric school bus batteries more sustainable, check out How to Ensure a Sustainable Future for Electric School Bus Batteries.